1. Field of the Invention
The invention relates to the recovery of useful products from sludge by-products of a pulp and paper operation. In particular, the present invention provides a system and process which can remove usable pulp, both low grade and high grade, from pulp sludge. In addition, heavy materials, such as rocks and scrap iron, as well as sand and grit are separated from the sludge for subsequent use or disposal.
2. Discussion of Background
Typically, after screening and pressing operations in a paper mill, a resultant waste sludge product remains which itself is not suitable for making paper or other products. In the past, systems have been developed to remove usable fibers from the sludge for subsequent use. For example, Maxham U.S. Pat. No. 5,137,599 discloses a system in which pulp and paper mill sludge can be converted to papermaking pulp. However, since the emphasis of Maxham is only upon recovering fiber usable in papermaking, only a small portion of the sludge is converted into a usable product. Thus, the remainder of the sludge is discarded, and the resultant small portion of usable pulp is reclaimed at a high cost. In addition to the large amounts of waste remaining and the high cost of reclaiming usable pulp in the Maxham system, the system is fairly complicated and requires the use of detergents.
Accordingly, a system and process are needed which can be used to economically reclaim usable pulp from sludge by-products of a pulp and paper mill. Preferably, such a system should be capable of removing other by-products from the sludge in addition to the removal of usable pulp. Further, such a system and process should most preferably be capable of producing or reclaiming different grades of pulp. Thus, the system should be capable of separating the sludge by-product into a number of usable products, thereby decreasing the discarded waste and also increasing the economical efficiency of the system.